Ammonium or nitrate: nitrogen forms in potato nutrition
The question “which nitrogen is better?” has no answer without soil conditions — and too much available N can delay tuber set and cut dry matter.
Potato Nutrition series · Part 04 of 24 · All parts in order
The question “which nitrogen is better?” has no answer without knowing the soil. Nitrate (NO₃⁻) is quickly available but easily leached, especially on sandy soils under sprinkler irrigation. Ammonium (NH₄⁺) is held better by the exchange complex but is gradually nitrified in warm, aerated soils. Urea first hydrolyses to ammonium; when surface-applied without incorporation, ammonia losses are possible.
California's CDFA guidelines recommend measuring residual soil nitrate as close to planting as possible and monitoring nutrition through the season, rather than relying only on the form stated on the fertilizer label. In waterlogged or cold soil the ratio of mineral forms and the speed of their transformation differ. pH, temperature, moisture, application method and the time until the next irrigation all matter.
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Nitrogen forms at a glance
| Form | Behaviour in soil | Main risk |
|---|---|---|
| Nitrate NO₃⁻ | Immediately available, mobile | Leaching on sands under irrigation |
| Ammonium NH₄⁺ | Held by the exchange complex | Gradual nitrification in warm soil |
| Urea | Hydrolyses to ammonium | Ammonia loss if not incorporated |
Conceptual comparison, no rates.
An excess of available nitrogen can delay tuber initiation and maturity, reduce dry matter and complicate harvest. Good early N supply should therefore not turn into an automatic late top-dressing. Programmes should be compared at the same total amount of applied nutrient and on crop quality, not only on the green mass of the canopy.
Geography and practical application
Minnesota and Idaho: high risk of nitrate leaching on irrigated sandy soils. Ireland: watch rainfall and mineralisation of organic matter. On the cool soils of north-western Russia, the speed at which N forms transform should be assessed separately.
Regional notes
- Russia & Central Asia (Kazakhstan, Uzbekistan): on irrigated land in Uzbekistan and Kazakhstan, nitrate moves with water; time N to irrigation rather than to the calendar.
- Latin America (Brazil, Andean countries): in warm, well-aerated tropical soils ammonium nitrifies quickly and nitrate leaches; cooler highland soils (Andes) keep more ammonium. Split applications are common practice.
- Africa (Kenya, Nigeria, Zimbabwe, Zambia): rain-fed highland crops lose N in heavy rains; match top-dressing to rainfall and canopy condition.
- South-East Asia (Vietnam, Thailand, Philippines): short cool-season crops need N early; late N risks delaying maturity before the warm season returns.
Agronomic guidance here is general practice; agree rates and timing with your agronomist.
Partner material: Uralchem products — conditional selection
UNIVERSAL 18:18:18+3MgO+TEFor in-season corrections during active growth, the catalogue lists the water-soluble UNIVERSAL 18:18:18+3MgO+TE. It should be used only where a deficiency of the corresponding nutrients is confirmed, and within the overall nitrogen budget.
Product images: Uralchem.
Where Uralchem supplies: Russia and the CIS, Latin America, Africa (through its distributor United Fertilizer Company Limited) and South-East Asia, where the company is developing distribution in Vietnam, Thailand and the Philippines. Availability of specific grades varies by country — check with the local distributor.
Not a rate recommendation — consult your agronomist.
Sources
- California Department of Food and Agriculture, Fertilization Guidelines: Potatoes.
- University of Minnesota Extension, Potato nutrient management research: five lessons.
- Stapley et al., Stacking and intersecting nitrogen 4Rs on potato, Soil Science Society of America Journal.
Partner data (Uralchem)
Potato Nutrition series · Part 04 of 24
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All 24 parts of the Potato Nutrition series in order
